Films made from cellulose ester fibers are useful for making molded products and as transparent sheeting. The films are typically composed of 100 percent cellulose acetate fibers and prepared by melting the cellulose acetate and casting or extruding it into a sheet form. This generally involves the use of solvents to prepare a dispersion of the cellulose acetate fibers so that an extremely thin sheet may be formed.
Thermoplastic films being made from 100 percent cellulose acetate fibers are typically used for applications requiring substantially transparent or lightly tinted materials. Once in film form whether by extrusion or other methods, the cellulose acetate film may be printed upon with the print resting on the surface of the film only. Typically a fast drying, specially formulated ink is required to prevent ink run-off or smearing. Additionally, these 100 percent cellulose acetate films are fairly expensive due to the extensive manufacturing processes required to produce cellulose acetate materials.
Another method of preparing cellulose acetate film which does not involve solvents and eliminates the extrusion/molding process is disclosed in U.S. Pat. No. 2,976,205 to Snead. These films are prepared from cellulose acetate webs that have been coated with a plasticizer and then subjected to heat and pressure. The cellulose acetate webs are formed on a wire of a papermaking machine from an aqueous dispersion of fibrous flocculated cellulose acetate. However, the cellulose acetate webs are extremely weak due to the extensive refining required to create uniformity in the dispersion. The webs are not capable of undergoing stressful processes such as printing prior to conversion into the film form. Once in the film form the printing problems as disclosed above still exist.
Thus, there exists a need in the art for a thermoplastic film that eliminates the use of solvents, is a simplified process, may be printed upon using conventional paper printing materials and techniques and is economically attractive to the end user.